The synthesis and structures of rare earth 2-fluorophenyl- and 2,3,4,5-tetrafluorophenyl-N,N '-bis(aryl)formamidinate complexes

Redox transmetallation/protolysis (RTP) reactions between free rare-earth metals (La, Nd, or Yb), Hg (C6F5)(2), and FFormH (FFormH = N,N'-bis(2-fluorophenyl)formamidine) in thf afforded four rare-earth complexes: trivalent [La(FForm)(3)(thf)(2)]center dot thf, [Nd(FForm)(3)(thf)(x)], [Yb(FForm)(3)(thf)] (when a slight excess of Yb was used), and divalent [Yb(FForm)(2)(thf)(2)] (when a large excess of Yb was used). With the exception of [Yb(FForm)(3)(thf)], the complexes did not readily crystallise from thf. However, crystallisation from either dme (La, Yb) or diglyme (Nd), produced single crystals of [La(FForm)(3)(dme)], [Yb(FForm)(2)(dme)(2)], and [Nd(FForm)(3)(diglyme)], respectively. A Nd complex of N,N'-bis(2,3,4,5-tetrafluorophenyl)formamidine (TFFormH): [Nd(TFForm)(3)(dme)], was also prepared by a similar RTP reaction, and was crystallised from dme. Heating the previously reported divalent TFForm complex: [Yb(TFForm)(2)(thf)(3)], in either PhMe or diglyme, separated out trace amounts of the trivalent complex [Yb(TFForm)(3)(thf)(2)] from PhMe, or the mixed oxidation state, solvent separated ion pair (SSIP) [Yb(TFForm)(diglyme)(2)][Yb (TFForm)(4)] from diglyme. The SSIP complex is the first crystallographically characterised trivalent ytterbium complex coordinating four discrete amidinate ligands